Light-activated compounds are well known and used in a variety of commercial applications. For example, such compounds are widely used in a variety of dental procedures including restoration work and teeth filling after root canals and other procedures requiring drilling. Several well-known dental compounds have been sold, for example, under the trade names of BRILLIANT LINE, Z-100, TPH, CHARISMA and HERCULITE & BRODIGY.
Dental compounds typically comprise liquid and powder components mixed together to form a paste. Curing of the compound requires the liquid component to evaporate, causing the composite to harden. In the past, curing has been accomplished by air drying, which has had the disadvantage of requiring significant time. This time can greatly inconvenience the patient. More recently, use of composite materials containing light-activated accelerators has become popular in the field of dentistry as a means for decreasing curing times. According to this trend, curing lights have been developed for dental curing applications. An example of such a curing light is illustrated by U.S. Pat. No. 5,975,895, issued Nov. 2, 1999 to Sullivan, which is hereby incorporated by reference.
Conventional dental curing lights generally employ tungsten filament halogen lamps that incorporate a filament for generating light, a reflector for directing light and often a filter for limiting transmitted wavelengths. For example, a blue filter may be used to limit transmitted light to wavelengths in the region of 400 to 500 nanometers (nm). Light is typically directed from the filtered lamp to a light guide, which directs the light emanating from an application end of the guide to a position adjacent to the material to be cured.
Filters are generally selected in accordance with the light activation properties of selected composite compound materials. For example, blue light may be found to be effective to excite composite accelerators such as camphoroquinine, which has a blue light absorption peak of approximately 470 nanometers (nm). Once excited, the camphoroquinine accelerator in turn stimulates the production of free radicals in a tertiary amine component of the composite, causing polymerization and hardening.
An increasing number of light activated compounds are being developed using a variety of photo initiators with different light properties For example, orthodontic adhesives have been produced with a phenol propanedione accelerator that undergoes free radical production in the presence of green light having a light absorption peak of approximately 440 nm. In order to be effectively used with a variety of compounds, it would therefore be desirable to have a curing light capable of delivering light of several colors.
As halogen lamps typically produce a broad light spectrum, these lights would seem to provide some advantage over other more monochromatic light sources, such as light emitting diodes (LEDs) and laser diodes (LDs). However, a problem with conventional halogen-based lights is that the lamp, filter and reflector degrade over time. This degradation is particularly accelerated, for example, by the significant heat generated by the halogen lamp. For example, this heat may cause filters to blister and cause reflectors to discolor, leading to reductions in light output and curing effectiveness. While heat may be dissipated by adding a fan unit to the light, the fan may cause other undesired effects (for example, undesirably dispersing a bacterial aerosol that may have been applied by the dentist to the patient's mouth). Alternate lamp technologies using Xenon and laser light sources have been investigated, but these technologies have tended to be costly, consumed large amounts of power and generated significant heat. Laser technologies have also required stringent safety precautions.
LEDs and LDs appear to be good alternates to halogen curing light sources, having excellent cost and life characteristics. Generating little heat, they also present less risk of irritation or discomfort to the patient. However, LEDs and LDs individually tend to produce relatively monochromatic light energy.
U.S. Pat. No. 6,331,111 to Cao discloses a curing light system incorporating a plurality of LEDs or LDs in a single curing light. The plurality of LEDs or LDs are located on a single heat sink to facilitate heat dissipation, and radiate light through a transparent focus dome or window toward a curing target. Cao notes that LEDs and LDs may be selected having different characteristic wavelengths in order to cure a variety of composite materials having photo initiators sensitive to these different characteristic wavelengths. However, Cao falls short of disclosing an efficient means for combining light energy from monochromatic light sources of a few colors in order to produce a broad, continuous spectrum of light energy for curing a variety of composite materials.